Cube of Zoroaster: A unique Achaemenid Monument

Cube of Zoroaster in the front large rock-cut tombs made for Achaemenid kings, Naghsh-e Rostam, Fars Province (photo by Faramarz)

The Cube of Zoroaster (also known as Ka'ba-ye Zartosht) is a 5th century BC Achaemenid-era tower-like construction at Naqsh-e Rustam, just northwest of Persepolis, in Fars Province. The structure is not actually a Zoroastrian shrine, nor are there reports of it ever having been a pilgrimage site. The structure, which is a copy of a sister building at Pasargadae, was built either by Darius I (r. 521-486 BC) when he moved to Persepolis, by Artaxerxes II (r. 404-358 BC) or Artaxerxes III (r. 358-338 BC). The wall surrounding the tower dates to Sassanid times.

The square tower is constructed of white limestone blocks, that - unlike those of the sister building - are held in place by iron cramps. Mortar was not used in its construction. Each side of the building is 7.25 meters wide. The 12.5 meter high structure has a slightly pyramidal roof and stands on a 1.5 meter high three-stepped plinth. Each face of the building is decorated with slightly recessed false windows of black limestone.

Photo by Roozbeh Taassob

The structure has one square inner chamber, 5.70 meter high and 3.70 meter wide, access to which is through a doorway with a decorated lintel in the upper half of the tower. The chamber was once accessible by a flight of steps, only the lower half of which has survived. The 1.70 meter wide and 1.90 meter high door was of solid stone that was originally firmly closed but has since disappeared.

From a reference to fire altars in a Sassanid-era inscription on the building it was inferred that the structure was once a fire altar, or perhaps as an eternal-flame memorial to the emperors whose tombs are located a few meters away. This theory has however since been rejected since the lack of cross-ventilation would have soon choked the flame. A later opinion suggested that both it and its sister building were safety boxes for the royal flags and other important belongings of the governing kings. Some experts believe that the monument was the home of a complete copy of the Avesta which had been written on 12,000 leather parchments.

Iranian archaeologist Reza Moradi Ghiasabadi has presented his own theory and described the monument as the world's most unique calendrical and astronomical observatory. According to him the month, day and even certain times of the day can exactly be determined by the sunlight shed on the structure and its resulting shadows.